The invention relates to a multi-layer, especially double-layer or three-layer paper machine wire for dewatering and sheetforming purposes comprising a multi-layer paper machine wire for dewatering and sheet forming, comprising an upper and a lower weft threads layer or an upper fabric and a lower fabric arranged one over the other and connected to one another by binding threads being fabric born threads, and extending in a special manner from one fabric layer into the respective other one fabric layer.
Such kind of paper machine wires are for instance known from the European Patent Specification 432,413 (U.S. Pat. No. 5,152,326). They form composite fabrics and are used for the wet end of paper making machines in order to dewater the fiber suspension fed over the pulp entry onto the wire and in order to lead the developing paper web to the press section of the paper machine.
The properties and characteristics of the surface of the paper which is to be manufactured depend largely with respect to its printing quality, smoothness and number of wire marks on the quality of the wire web. It is already known that the requested high wearing resistance of those wire webs does not or not most favourably harmonize with the requested surface quality of the paper and that in this connection the stability of the fabric, for instance, is reduced considerably, if the fineness of a wire is increased. On the other hand the requested recuction of wire marks, i.e. the undesired impressions of the yarn of the paper forming fabric into the surface of the paper web should be avoided. Many proposals have been made to solve these problems in order to manufacture a most favourable paper quality. Thus, for instance it was proposed to connect the several layers of the fabric, for instance a so-called three-layer fabric, by binding warp threads or binding weft threads using as binder threads two fabric born threads which are interwoven in a special manner with the respective fabric layer.
It was find out, however, that the problem of reducing wire marking cannot completely be solved by such a measure. Particularly in those cases, in which the wearing threads have a binding function according to which the exchangeably working threads are either filament supporting and binding or supporting, binding and wear contributing or filament supporting and abrasion contributing, these threads are the reason for wire marks continually created on the running side of the fabric.
Therefore, it is an object to be solved by the invention to reduce the creation of wire marks on paper machine wires by exchangeably working threads on the running side. According to a further object the wearing volume or capacity should be increased comparing it with that one of the known wires provided with exchangeably working or functioning threads.
These and other objects are solved according to the subject invention by the provision of a paper making wire, comprising a lower fabric manufactured of exchangeably functioning weft threads changing alternatively from the running side to the center position overlapping the warp threads within the region of exchange and protecting thereby the warp against wear and forming on extending between the fabric layers on the paper side an additional cushion against the creation of wire marks on the lower fabric.
The essential idea of the subject invention should be seen therein that the weft threads on the running side of two-layer or multi-layer paper machine wire are configured in form of threads working exchangeably between the center position and the running side of the fabric so that the lower fabric is protected in such an extent that its capability of forming wire marks with respect to dewatering pulses is essentially reduced so that the upper fabric is floating to some extent on the lower fabric, if two layer or three layer composite fabrics are used. Moreover, by the selected kind of binding the weft threads on the running side protect in case of double-layer fabrics on the running side the through-binding warp threads or in case of three-layer fabrics on the running side the lower warp threads against wearing.
Thus, under consideration of the above mentioned proposals an advantageous embodiment of the subject invention is characterized by leading in the region of exchange the throughbinding or binding, respectively, warp threads on the running side in the area of exchange below the alternatingly or exchangingly running weft threads.
According to a further advantageous embodiment of the invention the lower fabric comprises a satin binding or a twill binding or another binding derived from them.